Sep 12, 2012
QR codes printed using nanoparticle ink for security applications
QR codes have become a popular addition to posters, leaflets and magazines for sharing information such as web addresses. Now, researchers based at the South Dakota School of Mines and Technology, Rapid City, and the University of South Dakota, Vermillion, US, have introduced a version printed using nanoparticle inks that respond to near-infrared light. The design could be used for security purposes to send a covert message or reveal a hidden serial number, for example. Shining a laser over the printed area up-converts the inks into a visible pattern so that the information can be read just like a regular QR code using a smartphone.
The covert QR codes were printed using inks that contained nanoparticles of β-NaYF4:Yb3+ , Er3+ , which up-converts into green, and NaYF4:Yb3+, Tm3+, which up-converts into blue. The final solution comprised 1 or 2 weight percent of oleic acid-capped nanoparticles along with a binding agent poly(methyl methacrylate) in toluene/methyl benzoate solvent. The patterns are easy to print on a variety of substrates and form a rigid layer that contains an even dispersion of nanoparticles.
A variety of up-converting colours can be obtained by altering the lanthanide dopants. In their study, the scientists presented covert QR codes printed with additional security features. These extra details can be printed in many colours embedded within the QR codes, depending on the type of security needed. This approach provides another level of security as the additional features in the QR codes can be varied from micro to macro in size and excited using a single wavelength laser source.
Fabrication and testing
Full details can be found in the journal Nanotechnology.
About the author
This study was primarily conducted by the Group of Security Printing researchers in the Technology Development Lab (TDL) at South Dakota School of Mines and Technology (SDSM&T), Rapid City, and the University of South Dakota (USD), Vermillion, led by Dr Jon Kellar and Dr P Stanley May, respectively. The first author, Jeevan M Meruga, is a PhD candidate supervised by Dr Jon Kellar at SDSM&T, Rapid City. Jeevan M Meruga conducted the characterization of up-converting ink, printing, imaging and scanning of covert QR codes using up-converting nanoparticluate inks. The other collaborators include Dr P Stanley May and his student QuocAnh Luu from the University of South Dakota (USD), Vermillion. This collaborative team is involved in the synthesis of up-converting nanoparticles, up-converting ink formulation, characterization, printing of covert QR codes, up-converting the QR codes, imaging, scanning and characterization of the up-converting properties of the covert QR codes with the goal of making an economical, advanced and reliable security method for storing and transferring covert information in security applications.